On 07/24/2014 06:07 PM, Les Mikesell wrote:
> On Thu, Jul 24, 2014 at 7:11 PM, Lists <lists@xxxxxxxxxxxxxxxxxx> wrote:
>> I have a large disk full of data that I'd like to upgrade to SW RAID 1
>> with a minimum of downtime. Taking it offline for a day or more to rsync
>> all the files over is a non-starter. Since I've mounted SW RAID1 drives
>> directly with "mount -t ext3 /dev/sdX" it would seem possible to flip
>> the process around, perhaps change the partition type with fdisk or
>> parted, and remount as SW RAID1?
>>
>> I'm not trying to move over the O/S, just a data paritition with LOTS of
>> data. So far, Google pounding has resulted in howtos like this one
>> that's otherwise quite useful, but has a big "copy all your data over"
>> step I'd like to skip:
>>
>> http://sysadmin.compxtreme.ro/how-to-migrate-a-single-disk-linux-system-to-software-raid1/
>>
>> But it would seem to me that a sequence roughly like this should work
>> without having to recopy all the files.
>>
>> 1) umount /var/data;
>> 2) parted /dev/sdX
>> (change type to fd - Linux RAID auto)
>> 3) Set some volume parameters so it's seen as a RAID1 partition
>> "Degraded". (parted?)
>> 4) ??? Insert mdadm magic here ???
>> 5) Profit! `mount /dev/md1 /var/data`
>>
>> Wondering if anybody has done anything like this before...
>>
> Even if I found the magic place to change to make the drive think it
> was a raid member, I don't think I would trust getting it right with
> my only copy of the data. Note that you don't really have to be
> offline for the full duration of an rysnc to copy it. You can add
> another drive as a raid with a 'missing' member, mount it somewhere
> and rsync with the system live to get most of the data over. Then you
> can shut down all the applications that might be changing data for
> another rsync pass to pick up any changes - and that one should be
> fast. Then move the raid to the real mount point and either (safer)
> swap a new disk, keeping the old one as a backup or (more dangerous)
> change the partition type on the original and add it into the raid set
> and let the data sync up.
I would, of course, have backups. And the machine being upgraded is one
of several redundant file stores, so the risk is near zero of actual
data loss even if it should not work. :)
And I've done what you suggest: rsync "online", take apps offline,
rsync, swap, and bring it all back up. But the data set in question is
about 100 million small files (PDFs) and even an rsync -van takes a day
or more, downtime I'd like to avoid. A sibling data store is running
LVM2 so the upgrade without downtime is underway, another sibling is
using ZFS which breezed right through the upgrade so fast I wasn't sure
it had even worked!
So... is it possible to convert an EXT4 partition to a RAID1 partition
without having to copy the files over?
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